Intelligence endures When Ian Deary and his colleagues (2004) retested 80-year-old Scots, using an intelligence test they had taken as 11-year-olds, their scores across seven decades correlated +.66, as shown here. (Data from Deary et al., 2004.) When 207 survivors were again retested at age 90, the correlation with their age 11 scores was +.54 (Deary et al., 2013).